Local Immune Activation and Age Impact on Humoral Immunity in Mice, with a Focus on IgG Sialylation

Age alters the host's susceptibility to immune induction. Humoral immunity with circulating antibodies, particularly immunoglobulin G (IgG), plays an essential role in immune response. IgG glycosylation in the fragment crystallizable (Fc) region, including sialylation, is important in regulating the effector function by interacting with Fc gamma receptors (FcγRs). Glycosylation is fundamentally changed with age and inflammatory responses. We aimed to explore the regulation of humoral immunity by comparing responses to antigen-induced immune challenges in young and adult mice using a local antigen-induced arthritis mouse model. This study examines the differences in immune response between healthy and immune-challenged states across these groups. Our initial assessment of the arthritis model indicated that adult mice presented more severe knee swelling than their younger counterparts. In contrast, we found that neither histological assessment, bone mineral density, nor the number of osteoclasts differs. Our data revealed an age-associated but not immune challenge increase in total IgG; the only subtype affected by immune challenge was IgG1 and partially IgG3. Interestingly, the sialylation of IgG2b and IgG3 is affected by age and immune challenges but not stimulated further by immune challenges in adult mice. This suggests a shift in IgG towards a pro-inflammatory and potentially pathogenic state with age and inflammation.